Download in uniform motion flying at a speed of 600 mph.

Newton’s 1st Law
Newton’s 1st Law In his own words
• Isaac Newton said, “Every object continues in its
state of rest, or of uniform motion in a straight
line, unless it is compelled to change that state by
forces impressed upon it.”
– Objects at rest stay at rest.
– Objects in motion stay in motion.
– UNLESS another object applies a force upon the
object.
• THIS IS ALSO KNOWN AS THE LAW OF INERTIA
• This was actually first formulated by the great
Italian troublemaker Galileo Gaililei.
Well duh?
• Aristotle (and therefore most Greeks and
scientists before Gailileo) believed that objects
came to rest because that was their natural
place in the universe.
– Nothing is floating in the air…therefore objects
must want to return to the ground.
– However, we know now that this is often because
the Earth exerts a force upon objects.
Mass
• A measure of the amount of
inertia an object has.
• Inertia - The resistance of an
object to a change in velocity.
• Mass is also the amount of
matter that makes up an object.
• It is NOT the same as weight!
Weight
• Is the force upon an object due to gravity.
• Mass and weight are directly proportional to
each other, but weight depends on one
external factor:
Questions
1.
2.
3.
4.
5.
Which weighs more a 10 kg bag of gold or a 10 kg bag of feathers?
Which has more inertia?
What does an object at rest and an object in uniform motion have
in common?
What experiment can be conducted to distinguish rest from
uniform motion?
Suppose you’re sitting on an aisle seat in a passenger jet. You hold
a coin out in the aisle and drop it. The coin lands in the aisle
directly below your hand. From this you can conclude
A.
B.
C.
the jet is at rest on the runway.
the jet is in uniform motion flying at a speed of 600 mph.
neither of these: either motion described above could be happening.